Sub-lithographic semiconductor structures with non-constant pitch

ABSTRACT

Fin structures and methods of manufacturing fin structures using a dual-material sidewall image transfer mask to enable patterning of sub-lithographic features is disclosed. The method of forming a plurality of fins includes forming a first set of fins having a first pitch. The method further includes forming an adjacent fin to the first set of fins. The adjacent fin and a nearest fin of the first set of fins have a second pitch larger than the first pitch. The first set of fins and the adjacent fin are sub-lithographic features formed using a sidewall image transfer process.

FIELD OF THE INVENTION

The invention relates to semiconductor structures and, moreparticularly, to fin structures and methods of manufacturing finstructures using a dual-material sidewall image transfer mask to enablepatterning of sub-lithographic features.

BACKGROUND

As critical dimensions in integrated circuit fabrication descend belowwidths printable employing deep ultraviolet (DUV) lithographyprocessing, fabrication processes are turning to Sidewall Image Transfer(SIT) techniques. The SIT techniques provide a way to build structureshaving pitch and width which are not otherwise possible withconventional DUV lithography processes. The SIT process can be used tomanufacture, for example, fin structures, e.g., FinFETs, with a constantpitch and width.

SUMMARY

In one or more embodiments of the invention, a method of forming aplurality of fins comprises forming a first set of fins having a firstpitch. The method further comprises forming an adjacent fin to the firstset of fins. The adjacent fin and a nearest fin of the first set of finshave a second pitch larger than the first pitch. The first set of finsand the adjacent fin are sub-lithographic features formed using asidewall image transfer process.

In one or more embodiments of the invention, a method comprises formingan etch stop layer on a semiconductor material and forming a mandrel onthe etch stop layer. The method further comprises forming sidewallspacer material on the mandrel and removing the mandrel. The methodfurther comprises forming filler spacers on the sidewall spacermaterial. The method further comprises forming fill material between thefiller spacers. The method further comprises removing the filler spacersand portions of the semiconductor material below the filler spacers toform: a first set of structures comprising the sidewall spacers, theetch stop layer and the semiconductor material, and a second set ofstructures comprising the fill material and the semiconductor material.The method further comprises alternately forming a mask over groupingsof a plurality of the first set of structures and the second set ofstructures, and alternating etching material from unprotected ones ofthe first set of structures and the second set of structures to form finstructures of the semiconductor material with a non-constant pitch.

In one or more embodiments of the invention, a structure comprises afirst set of fins having a first pitch and an adjacent fin to the firstset of fins. The adjacent fin and a nearest fin of the first set of finshave a second pitch larger than the first pitch. The first set of finsand the adjacent fin are sub-lithographic features formed fromsemiconductor material on an oxide layer.

In another aspect of the invention, a design structure tangibly embodiedin a machine readable storage medium for designing, manufacturing, ortesting an integrated circuit is provided. The design structurecomprises the structures of the present invention. In furtherembodiments, a hardware description language (HDL) design structureencoded on a machine-readable data storage medium comprises elementsthat when processed in a computer-aided design system generates amachine-executable representation of the fin structures, which comprisesthe structures of the present invention. In still further embodiments, amethod in a computer-aided design system is provided for generating afunctional design model of the fin structures. The method comprisesgenerating a functional representation of the structural elements of thefin structures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIGS. 1-9 show processing steps and respective structures in accordancewith aspects of the present invention;

FIG. 10 shows a top view of the structure of FIG. 9, in accordance withaspects of the present invention;

FIGS. 11-15 show processing steps and respective structures inaccordance with additional aspects of the present invention; and

FIG. 16 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test.

DETAILED DESCRIPTION

The invention relates to semiconductor structures and, moreparticularly, to fin structures and methods of manufacturing such finstructures. In embodiments, the fin structures can be fabricated using adual-material sidewall image transfer (SIT) mask to enable patterning ofsub-lithographic features. More specifically, the present invention usesa SIT-squared technique or variation thereof to pattern sub-lithographicfeatures using 1× lithography processes. A SIT-squared technique usestwo sets of feature-defining spacers, which enable 4× pitch reduction,e.g., fins can obtain dimensions of about 6-8 nm width and space.Advantageously, the present invention enables the patterning ofsub-lithographic fins with a non-constant pitch or substantiallyconstant pitch depending on mandrel and conformal coating implementedwith the present invention, while providing improved fin-to-fin widthcontrol.

In more specific embodiments, an etch stop layer (e.g., HfO₂ or SiO₂) isprovided on a substrate (e.g., SOI layer). Mandrels are formed on theetch stop layer, which comprise material, e.g., Si₃N₄ or SiO₂, that canbe selectively etched to the etch stop layer. Sidewall spacers areformed on the mandrels, which can be for example, amorphous silicon(aSi). The mandrels are stripped to expose the etch stop layer, andleaving the sidewall spacers. Filler spacers (e.g., SiO₂) are formed onboth sides of the sidewall spacers, and fill material is depositedbetween the filler spacers. The fill material is of a different materialthan the filler spacers, e.g., Si₃N₄. The filler spacers can then beremoved, in addition to the etch stop layer and the SOI layer which waspreviously protected by the filler spacers. Thereafter, throughselective masking operations, sub-lithographic fins of different spacingor pitch can be formed on the substrate.

FIG. 1 shows a structure and respective processing steps in accordancewith aspects of the present invention. In embodiments, the structure 5includes a substrate 10. In embodiments, the substrate 10 is a siliconon insulator (SOI) formed using conventional processes such as waferbonding or SiMOX. In embodiments, the substrate 10 includes a BOX layer12. It should be understood by those of skill in the art that the BOXlayer 12 can be provided on an underlying substrate, e.g., silicon, andis formed of an oxide based material. A silicon based layer 14 is formedon the BOX layer 12. In embodiments, the layer 14 can be, for example,Silicon or SiGe or other known semiconductor materials. An etch stoplayer 16 is deposited on the layer 14. In embodiments, the etch stoplayer 16 can be HFO₂ or SiO₂.

A mandrel 18 is formed on the etch stop layer 16, using conventionaldeposition, lithography and etching processes. For example, a mandrelmaterial, e.g., Si₃N₄ or SiO₂, is deposited on the etch stop layer 16using conventional chemical vapor deposition (CVD) processes. A resistis formed on the mandrel material, and exposed to light to form apattern (openings). A reactive ion etching is performed through theopenings to form the mandrels 18. In embodiments, the mandrels 18 canhave a width of about 22 nm, and a spacing of about 34 nm (pitch ofabout 56 nm); although other dimensions are also contemplated by thepresent invention.

In FIG. 2, sidewall spacers 20 are formed on the sides of the mandrels18. In embodiments, the sidewall spacers 20 are amorphous silicon (orother material that is different than the mandrels 18 and othersubsequently formed structures as discussed below, in order to allowselective etching). In embodiments, the sidewall spacers 20 can beformed by using conventional deposition processes known to those ofskill in the art. The sidewall spacers 20 can have a width of about 6nm; although, other dimensions are also contemplated by the presentinvention.

As shown in FIG. 3, the mandrels are removed or stripped using aconventional etching process, selective to the mandrel material. Inembodiments, the etch stop layer underlying the mandrels is alsoremoved, using a selective pull down or etching process. Filler spacers22 are formed on the sidewalls of the sidewall spacers 20, extendingdirectly on to the surface of the layer 14. The filler spacers 22 areformed using a conventional conformal deposition process. Inembodiments, the filler spacers 22 are SiO₂ or other material that isdifferent than the material forming the sidewall spacers 20. Inembodiments, the filler spacers 22 can be formed to a width of about 8nm, leaving a space 21 therebetween of about 6 nm; although otherdimensions are also contemplated by the present invention.

In FIG. 4, the space 21 is filled with fill material 24. In embodiments,the fill material 24 is Si₃N₄, or other material that is different thanthe material forming the sidewall spacers 20 and the filler spacers 22.The fill material 24 can be deposited using a conventional conformaldeposition process, for example. Any fill material 24 that was depositedon top of the sidewall spacers 20 and the filler spacers 22 can beremoved using, for example, a conventional etching process. Inembodiments, the sidewall spacers 20 can also be pulled down to maintaincontrol of the aspect ratio.

As shown in FIG. 5, the filler spacers are removed using a selectiveetching process. For example, in embodiments, the selective etchingprocess is selective to the material of the filler spacers, e.g., SiO₂.That is, the etchant chemistry will not remove the sidewall spacers 20or the fill material 24. This being the case, the sidewall spacers 20will protect the underlying etch stop layer 16, which will be utilizedin later selective etching processes. In further embodiments, theexposed portions of the layer 14 are removed. In this process, the BOX12 will act as a stop layer, as the etchant chemistry is selective tothe material of layer 14. This process forms a space 26 between theremaining structures.

FIG. 6 shows additional processes and a respective structure inaccordance with aspects of the present invention. In FIG. 6, thestructures thus formed are provided at spaces labeled sequentially: 0,1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 0. As shown in FIG. 6, a mask 28is formed over selective ones of the structures, exposing other ones ofthe structures, e.g., exposing selective sidewall spacers 20. Inparticular, the mask 28 is formed over the structures, in spaces: 1, 1,0, 1, 0, 1, 0, 1, 1. Additionally, the mask 26 is formed over thestructures, in spaces: 1, 1, 0. It should be understood that the mask 28does not have to completely cover (e.g., be completely aligned with) theend structures 100, as they are protected by the fill material 24, e.g.,Si₃N₄. In fact, the mask 28 can be misaligned by 2× widths of thestructures, as the fill material 24, e.g., Si3N4, will protect thesestructures during subsequent etching processes.

An etching process is then performed to remove any exposed (unprotected)sidewall spacer material, e.g., amorphous silicon or other material thatis different than the fill material 24, e.g., Si₃N₄. In embodiments, theetching process will stop at the etch stop layer, which can beselectively removed by a second etching process. In this way, siliconislands 200 are formed on the BOX 12. The mask 28 can then be removedusing conventional oxygen ashing processes, for example.

In FIG. 7, another mask 30 is formed over the silicon islands 200, inaddition to another grouping of structures. For example, in thisembodiment, the mask 30 is formed over the structures in spaces 0, 1, 1.Additionally, the mask 30 is formed over the structures in spaces 1, 1,0, 1, 1. It should be understood that the mask 30 does not have tocompletely cover (e.g., be completely aligned with) the end structures210, which are protected by the sidewall spacers 20. In fact, the mask30 can be misaligned by 2 x widths of the structures 210. An etchingprocess is then performed to remove any exposed fill material 24, e.g.,Si₃N₄, resulting in silicon islands 200 a. The etching process will notaffect the sidewall spacers 20, as this etching process is selective tothe fill material 24, e.g., Si₃N₄. The mask 30 can then be removed usingconventional oxygen ashing processes, for example.

In FIG. 8, any remaining sidewall spacers 20 and the silicon fins (200and 200 a) can be removed, using a selective etch chemistry to thesidewall spacers 20 and the fins (200 and 200 a). As the sidewallspacers and the silicon fins are both composed of silicon material, asingle etching process selective to both the sidewall spacers and thesilicon fins is possible. In this etching process, the fill material 24,e.g., Si₃N₄ and the etch stop layer 16 will provide protection to theremaining respective structures 300 (composed of an underlying siliconmaterial). In this way, all structures in the “0” space can be removed.

In FIG. 9, the fill material 24, e.g., Si₃N₄ and the etch stop layer 16can be removed through a selective etching process. For example, thefill material 24, e.g., Si₃N₄, can be removed with a first etchantchemistry, and the etch stop layer 16 can be removed with a secondetchant chemistry. The etching process will leave sub-lithographicfeatures 400, e.g., silicon fins at spaces “1”, with a non-constant orsubstantially constant pitch, while providing improved fin-to-fin widthcontrol.

FIG. 10 is a top view of the structure shown in FIG. 9. The finstructures 400 shown herein are sub-lithographic features. As shown inFIG. 10, the fin structure 400 can have a pitch of either approximately30 nm or 60 nm; although other dimensions are also contemplated by thepresent invention. For example, the fin structures 400 can have a pitchof approximately 90 nm or 120 nm, in combination with fin structureshaving a pitch of 30 nm. It should be further understood by those ofskill in the art that due to photolithography overlay issues, thedimensions of the first pitch, e.g., 30 nm, the second pitch, e.g., 60nm, or other pitches may have slight variations. Accordingly, thepitches between fins, as described below, may be equal or substantiallyequal to one another in view of such overlay issues.

As an illustrative example, starting from the left side of FIG. 10, thefirst set of fins (labeled “A” and “B”) have a first pitch, e.g., 30 nm,and an adjacent fin (labeled “C”) to the first set of fins “A” and “B”has a second pitch larger than the first pitch, e.g., 60 nm. The nexttwo fins “D” and “E” are separated by a pitch which is the same orsubstantially the same dimensions of the second pitch, e.g., 60 nm. Thelatter fin “E” forms part of another set of fins (“E” and “F”) which hasa pitch of the same or substantially the same dimensions as the firstpitch, e.g., 30 nm. This pair of fins “E” and “F” is adjacent to anotherpair of fins (“G” and “H”). The pitch of the last pair of fins “G” and“H” is the same or substantially the same as the pitch of the first setof fins “A” and “B”, e.g., 30 nm; whereas, a pitch between the fins “F”and “G” are the same or substantially the same to the second pitch,e.g., 60 nm. Following the fin “G”, a pitch of more than 60 nm (as twofin structures were removed) may be possible. Such a larger pitch isalso possible between any of the fins, using the combination ofmaterials and alternate etching and masking steps as disclosed herein,and which should be understood by those of skill in the art.Advantageously and accordingly, the pitch between the fin structures canbe irregular or non-constant by implementing the processes of thepresent invention.

Accordingly, by implementing the processes of the present invention, asingle mask can be employed to define the location of the SIT fins. Finsso-defined will not all have width tolerances of sidewall depositions,and will have “pitch walk” in the original mandrel layer resulting in anon-constant fin width. If so desired, a second mandrel mask can beemployed to define a second set of fin mandrels, as shown in FIGS.11-14.

FIGS. 11-14 show processing steps and respective structures according toadditional aspects of the present invention. FIG. 11 shows a structure5′ similar to that shown in FIG. 1. For example, the structure 5′includes a substrate 10 comprising a BOX layer 12 and a silicon basedlayer 14 formed on the BOX layer 12. An etch stop layer 16 is depositedon the layer 14. A mandrel 18 is formed on the etch stop layer 16, usingconventional deposition, lithography and etching processes as discussedabove. It should be recognized by those of skill in the art that theetching steps may be, for example, a reactive ion etching (RIE), usingdifferent chemistries depending on the materials to be etched.

In FIG. 12, sidewall spacers 20 are formed on the sides of the mandrels18. In embodiments, the sidewall spacers 20 are amorphous silicon (orother material in order to allow selective etching). In embodiments, thesidewall spacers 20 can be formed using conventional depositionprocesses known to those of skill in the art. The sidewall spacers 20can have a width of about 6 nm; although, other dimensions are alsocontemplated by the present invention.

In FIG. 13, the mandrels are removed using a selective etching process,leaving the sidewall spacers 20. A fill material 32, e.g., Si₃N₄, isdeposited over the sidewall spacers 20. In embodiments, the fillmaterial 32 is planarized using conventional chemical mechanicalpolishing (CMP) processes. In embodiments, the fill material 32 shouldremain over the sidewall spacers 20, as a cap. In embodiments, anadditional cap layer of fill material can also be deposited andplanarized. A second mandrel 18′ of amorphous silicon is deposited andpatterned on the planarized fill material 32. In embodiments, the secondmandrel 18′ is aligned with, e.g., formed over, the sidewall spacers 20.Sidewall spacers 20′ are then formed on the second mandrel 18′, usingconventional conformal deposition processes. In embodiments, thesidewall spacers 20′ are formed of SiO₂ based material.

In FIG. 14, the second mandrel 18′ and the fill material 32, e.g.,Si₃N₄, are removed (etched using conventional RIE processes), where theSiO₂ based material of the sidewall spacers 20′ act as a maskingmaterial. In embodiments, the second mandrel 18′ and the fill material32 can be removed using selective etchants.

In FIG. 15, the sidewall spacers 20′ are removed, using a selectiveetching process. The process then continues with the processes shown inFIG. 5, for example.

FIG. 16 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test. FIG. 16 shows a block diagram of anexemplary design flow 900 used for example, in semiconductor IC logicdesign, simulation, test, layout, and manufacture. Design flow 900includes processes, machines and/or mechanisms for processing designstructures or devices to generate logically or otherwise functionallyequivalent representations of the design structures and/or devicesdescribed above and shown in FIGS. 1-15. The design structures processedand/or generated by design flow 900 may be encoded on machine-readabletransmission or storage media to include data and/or instructions thatwhen executed or otherwise processed on a data processing systemgenerate a logically, structurally, mechanically, or otherwisefunctionally equivalent representation of hardware components, circuits,devices, or systems. Machines include, but are not limited to, anymachine used in an IC design process, such as designing, manufacturing,or simulating a circuit, component, device, or system. For example,machines may include: lithography machines, machines and/or equipmentfor generating masks (e.g. e-beam writers), computers or equipment forsimulating design structures, any apparatus used in the manufacturing ortest process, or any machines for programming functionally equivalentrepresentations of the design structures into any medium (e.g. a machinefor programming a programmable gate array).

Design flow 900 may vary depending on the type of representation beingdesigned. For example, a design flow 900 for building an applicationspecific IC (ASIC) may differ from a design flow 900 for designing astandard component or from a design flow 900 for instantiating thedesign into a programmable array, for example a programmable gate array(PGA) or a field programmable gate array (FPGA) offered by Altera® Inc.or Xilinx® Inc.

FIG. 16 illustrates multiple such design structures including an inputdesign structure 920 that is preferably processed by a design process910. Design structure 920 may be a logical simulation design structuregenerated and processed by design process 910 to produce a logicallyequivalent functional representation of a hardware device. Designstructure 920 may also or alternatively comprise data and/or programinstructions that when processed by design process 910, generate afunctional representation of the physical structure of a hardwaredevice. Whether representing functional and/or structural designfeatures, design structure 920 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer. When encoded on a machine-readable datatransmission, gate array, or storage medium, design structure 920 may beaccessed and processed by one or more hardware and/or software moduleswithin design process 910 to simulate or otherwise functionallyrepresent an electronic component, circuit, electronic or logic module,apparatus, device, or system such as those shown in FIGS. 1-15. As such,design structure 920 may comprise files or other data structuresincluding human and/or machine-readable source code, compiledstructures, and computer-executable code structures that when processedby a design or simulation data processing system, functionally simulateor otherwise represent circuits or other levels of hardware logicdesign. Such data structures may include hardware-description language(HDL) design entities or other data structures conforming to and/orcompatible with lower-level HDL design languages such as Verilog andVHDL, and/or higher level design languages such as C or C++.

Design process 910 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown in FIGS. 1-15 to generate a netlist980 which may contain design structures such as design structure 920.Netlist 980 may comprise, for example, compiled or otherwise processeddata structures representing a list of wires, discrete components, logicgates, control circuits, I/O devices, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign. Netlist 980 may be synthesized using an iterative process inwhich netlist 980 is resynthesized one or more times depending on designspecifications and parameters for the device. As with other designstructure types described herein, netlist 980 may be recorded on amachine-readable data storage medium or programmed into a programmablegate array. The medium may be a non-volatile storage medium such as amagnetic or optical disk drive, a programmable gate array, a compactflash, or other flash memory. Additionally, or in the alternative, themedium may be a system or cache memory, buffer space, or electrically oroptically conductive devices and materials on which data packets may betransmitted and intermediately stored via the Internet, or othernetworking suitable means.

Design process 910 may include hardware and software modules forprocessing a variety of input data structure types including netlist980. Such data structure types may reside, for example, within libraryelements 930 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 32 nm,45 nm, 90 nm, etc.). The data structure types may further include designspecifications 940, characterization data 950, verification data 960,design rules 970, and test data files 985 which may include input testpatterns, output test results, and other testing information. Designprocess 910 may further include, for example, standard mechanical designprocesses such as stress analysis, thermal analysis, mechanical eventsimulation, process simulation for operations such as casting, molding,and die press forming, etc. One of ordinary skill in the art ofmechanical design can appreciate the extent of possible mechanicaldesign tools and applications used in design process 910 withoutdeviating from the scope and spirit of the invention. Design process 910may also include modules for performing standard circuit designprocesses such as timing analysis, verification, design rule checking,place and route operations, etc.

Design process 910 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 920 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 990.

Design structure 990 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g. information stored in a IGES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 920, design structure 990 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown in FIGS. 1-15. In one embodiment, design structure 990may comprise a compiled, executable HDL simulation model thatfunctionally simulates the devices shown in FIGS. 1-15.

Design structure 990 may also employ a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design data structures). Designstructure 990 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by amanufacturer or other designer/developer to produce a device orstructure as described above and shown in FIGS. 1-15. Design structure990 may then proceed to a stage 995 where, for example, design structure990: proceeds to tape-out, is released to manufacturing, is released toa mask house, is sent to another design house, is sent back to thecustomer, etc.

The method as described above is used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed:
 1. A method, comprising: forming an etch stop layer ona semiconductor material; forming a mandrel on the etch stop layer;forming sidewall spacer material on the mandrel; removing the mandrel;forming filler spacers on the sidewall spacer material; forming fillmaterial between the filler spacers; removing the filler spacers andportions of the semiconductor material below the filler spacers to form:a first set of structures comprising the sidewall spacers, the etch stoplayer and the semiconductor material, and a second set of structurescomprising the fill material and the semiconductor material; andalternately forming a mask over groupings of a plurality of the firstset of structures and the second set of structures, and alternatingetching material from unprotected ones of the first set of structuresand the second set of structures to form fin structures of thesemiconductor material with a non-constant pitch.
 2. The method of claim1, wherein the alternately forming the mask and etching comprises:forming a mask over a first grouping of the plurality of the first setof structures and the second set of structures, with at least one of thefirst set of structures being unprotected; removing the sidewallmaterial and the etch stop layer from the at least one unprotected firstset of structures to form semiconductor islands; removing the mask;forming another mask over another group of the plurality of the firstset of structures and the second set of structures and the semiconductorislands, leaving unprotected a grouping of the first set of structuresand the second set of structures; removing the fill material from theunprotected second set of structures; removing the sidewall spacermaterial from the unprotected first set of structures; removing theanother mask; removing the semiconductor islands; and removing anyremaining etch stop layer and fill material to form the fin structuresof the semiconductor material with a non-constant pitch.
 3. The methodof claim 2, wherein the fill material and the etch stop layer preventremoval of the semiconductor material of the fins during the removingthe semiconductor islands.
 4. The method of claim 1, wherein the firstset of structures are alternating with the second set of structures. 5.The method of claim 1, wherein the removing the mandrel includesremoving the etch stop layer underneath the mandrel.
 6. The method ofclaim 1, wherein the forming the filler spacers and fill material areformed directly on the semiconductor material, where the etch stop layerwas removed.
 7. The method of claim 1, wherein the fill material is amasking layer of different material than the etch stop layer and thesidewall spacer material such that the alternating etching can beperformed selectively.